SU904093A1 - Device for automatic compensation for capacitive current at single-phase earthing - Google Patents

Description

To achieve this goal, a device for automatic compensation of capacitive current in a single-phase earth fault, containing a series-connected amplitude detector, a band-pass filter, as well as a relay link, a synchronous detector, a low frequency filter and an actuator with a relay characteristic, is equipped with a mode difference unit, a heater, a differentiator and a block; an intermittent arc mode, the block input being connected to the zero-sequence voltage sensor and the sensor m zheny network phase voltage, and its output via the first logarithm ator connected to the input of the amplitude detector; the second output is via an intermittent-arc mode block. with a second input of the low-pass filter, and a differentiator is connected between the band-pass filter and the relay link.

The drawing shows a functional diagram of an apparatus for automatically compensating for capacitive currents during single-phase earth faults.

The circuit contains a mode detection unit 1, the inputs of which are supplied with the voltage of the network phases A, B, C, network asymmetry voltage SUp, logarithm 2, amplitude detector 3, band-pass filter 4, differentiator 5, relay link 6, synchronous detector 7, filter 8 low frequency, executive authority 9 with relay characteristic and block 0 of intermittent arc mode.

The device works as follows.

The mode discrimination unit 1, to the inputs of which the asymmetry voltage of the zero-sequence circuit and the mains phase voltage is applied, allows the setting of an arc signal to be detected by the first channel, which includes logari (| mator 2, a small detector 3, band-pass filter 4, differentiator 5, relay link 6, synchronous detector 7, low-pass filter 8, actuator 9 with a relay characteristic. In the intermittent arc single-phase closure network, the mode discrimination unit 1 switches the second channel consisting of the intermittent arc mode unit 10, the low-frequency filter 8 and the burdock actuator 9. The logarifmator 2 is built as an amplifier covered by non-linear feedback, allowing one to realize a logarithmic characteristic by approximating it with several sections. At the same time, the input signals of different levels are transmitted with different gain factors, which L is the dynamic range of variations in the input signal logarifmatora 2, which entered the amplitude detector 3, is subjected to amplitude detection at the carrier frequency. The band-pass filter 4 filters the high-frequency component at the output of the amplitude detector 3. The next differentiator 5 then differentiates the output signal from the band-pass filter 4. Re; the link element 6 performs the functions of the first channel transmission coefficient stabilizer. At its output, a sequence of rectangular pulses of constant amplitude and different porosity appears, the value of which depends on the accuracy of the tuning of the arcing coil and is equal to two when fine tuned. The use of relay-like reference signals and relay signals from the run-out of the relay link 6 makes it very simple and accurate to organize their synchronous detection. At the output of the synchronous detector, a sequence of rectangular opposite-polar oscillations appears, which is fed to the first input of the low-frequency filter 8, while the second input, which is the output of the second channel, is turned off. The low-frequency filter 8 is designed to filter the oscillatory component twice frequency and the selection of a constant component of the signal from the output of the synchronous detector 7. Depending on the polarity of the signal at the output of the low-frequency filter 8, the actuator 9 with a relay characteristic that zveno.s put a dead zone is generated a signal whose polarity determines the direction of movement of the system to the extreme kontupa zero sequence network. When fine tuning the arc-suppressing coil, the signal at the output of the low-frequency filter 8 is a sequence of pulses whose amplitude is no more than the dead zone of the actuator 9 with a relay characteristic, which is determined from the accuracy condition. settings of arc suppression catupzhi (no more than 3-5%).

When a single-phase ground fault occurs in the network, the operation of the first channel corresponds to that described in normal mode, with the only difference that the mode discriminator 1 supplies the input of the logarithm 2 to the voltage on the damaged phase of the network and inverts the feedback sign of the first channel, since it is tuned to an extremum minimum in contrast to the normal mode, where the extremum is maximum.

In the event of intermittent arc single-phase closure of the network to the ground, the mode discrimination unit 1

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blocks the first channel, disconnecting the input of the logarithm 2 and the output of the synchronous detector 7, and connects the second channel. In this mode, from block 1 of the mode detection, the asymmetry voltage of the 3Uo network is applied to the input of the block of the intermittent arc 10. The intermittent arc mode unit 10 provides a measurement of the deviations of the frequency itself of the zero-sequence network loop at the moments of dead-time pauses from the nominal network frequency of 50 Hz. The signal from the output of the block 10 of the intermittent arc mode is fed to the inlet of the low-frequency filter 8. In this case, the first input of filter 8 is disabled. From the output of the low-frequency filter 8, the signal in the form of a sequence of opposite-polarity pulses, the duration and polarity of which is determined respectively by the pauses between MI arc and detuning compensation relative to resonance, goes to the input of the actuator. oprawa 9 with a relay characteristic, which, depending on the polarity of the input signal, generates a signal that controls the change in the value of the coil's inductance depending on the tuning accuracy. With fine tuning, the signal at the output of the intermittent arc mode block 10 is almost zero.

Introduction to the circuit of the first channel of the logarithm increases the sensitivity of the system at low signal levels at the output of the control object and deactivates: the difference in the values of the input signals, during normal operation and with a single-phase short circuit, to earth, which can differ hundreds of times. This ensures that the system functions normally with significant changes in the input signal level. The introduction of a differentiator into the first channel after the bandpass filter allows to significantly increase the overall sensitivity of the system during its operation in normal mode and with a deaf single-phase circuit of the network to the ground. The proposed automatic compensation of capacitive currents with single-phase closures in the network effectively works not only in normal mode and with blind closures, but also when an intermittent arc closure appears in the network. All this allows the device to perform accurate resonant tuning of the arcing coil throughout the entire life of the device, which significantly improves the reliability of the network, uninterrupted power supply to consumers, and reduces the residual currents in the circuit to the minimum defined by the active component of the network’s network succession circuit. and higher harmonics and, therefore, improved electrical safety conditions for the electrical installation personnel.

Claims (2)

Invention Formula A device for automatic compensation of capacitive current in a single-phase earth fault, containing a series-connected amplitude detector, a band-pass filter, as well as a relay link, a synchronous detector, a low-pass filter and an actuator with a relay characteristic, characterized in that by ensuring that the device operates when a single-phase arc closure mode appears in the network and its sensitivity is controlled at small input levels It is equipped with a mode discriminator, a logarithm, a differentiator and an intermittent arc mode unit, the input of the mode discriminator is connected to a zero-sequence voltage sensor and phase network voltage sensors, and its first output is connected to an amplitude detector 3 input through a logarithmizer, the second output is through a block of intermittent arc mode with the second input of the low-frequency filter, and a differentiator is connected between the bandpass filter and the relay link. Sources of information taken into account in the examination 1. The author's certificate of the USSR № 424275, cl. H 02 J, 1974, 2. USSR author's certificate №612328, cl. H 02 H 1/02, 1978.